Spacer For A Heat Exchanger And Associated Heat Exchanger

ABSTRACT

A spacer ( 7 ) for an air heater comprises a predefined number of planar walls ( 13; 113 ) that are substantially parallel and are connected two-by-two by folds ( 15 ). The planar walls ( 13; 113 ) include a plurality of louvers ( 17   1   , 17   2 ) that are substantially inclined relative to the general plane (P) defined by the planar wall ( 13; 113 ). The planar wall ( 13; 113 ) further includes at least one strap ( 19; 119   1   , 119   2   , 119   3   , 119   4 ) having longitudinal sides ( 21 ) that extend parallel to the planar wall ( 13; 113 ) and lateral sides ( 23 ) that are linked to the planar wall ( 13; 113 ) by means of at least one connecting rail ( 24 ). An air heater comprises a heat exchange bundle comprising a stack of parallel tubes ( 5 ) for the circulation of the fluid, the tubes having the width (l 1 ) of a tube, and a plurality of such spacers ( 7 ) disposed respectively between two tubes ( 5 ).

The invention belongs to the field of ventilation, heating and/or air conditioning systems for an electric or hybrid automobile.

The invention has as its object a spacer for an air heater interacting with such an installation and an associated air heater.

An electric or hybrid automobile, of which the propulsion is provided at least partially by an electric motor, is commonly equipped with a system of ventilation, heating and/or air conditioning for the purpose of modifying the aerothermic parameters of the air in the interior of the passenger compartment of the vehicle by delivering a flow of conditioned air to the interior of the passenger compartment.

Such a conditioning system may be used, for example, during the summer in order to meet a need for cooling of the passenger compartment, but also during the winter, for example, in order to meet a need for heating of the passenger compartment.

Generally, the conditioning system includes at least one air heater that is capable of operating in condenser mode or in evaporator mode, depending on the needs.

The air heater generally includes a bundle of, for example, corrugated tubes and spacers, also referred to as corrugated fins, arranged between the tubes of the bundle and attached to these tubes, usually by brazing, by their respective folds.

The bundle of tubes is usually swept by a gas stream such as a flow of air which will exchange heat with another fluid, usually a heat transfer medium, that is circulating inside the tubes of the bundle.

The corrugated spacers are generally formed from a metal strip and comprise an assembly of planar walls, connected two-by-two by folds in order to form alternate corrugations.

Already familiar are spacers in which each of the planar walls is equipped with a plurality of inclined louvers that are produced by cutting and forming the strip. The principal function of the louvers that are included in the corrugated spacers is to improve the thermal exchange by the active, thorough mixing of the flow of air which sweeps the bundle, by so doing forcing a flow of air through the louvers.

Furthermore, such an air heater may be capable of operating in evaporator or condenser mode and is arranged, for example, at the level of the front surface of the vehicle for a thermal exchange between the fluid and a flow of outside air to the vehicle.

In particular, in order to meet the needs for heating, a known solution is to use the conditioning system in heat pump mode.

In this case, the external air heater operates in evaporator mode.

The disadvantage of such a solution when it is implemented in winter conditions is the risk of icing of the external air heater when operating in evaporator mode as a result of the condensation of the water vapor in the air and its cooling in contact with the walls. In particular, the spacers in the interior of the air heater may become iced up.

This has the effect of reducing significantly the thermal exchanges within this air heater, and, as a consequence, the output and the efficiency of the conditioning system.

Already familiar from the prior art is a solution which involves the use of the air heater in condenser mode. In order to do this, the conditioning system is generally used in air conditioning mode. The air heater in condenser mode is accordingly traversed by hot gases, which permits the deicing.

However, this solution also does nothing in terms of suppressing the retention of water in the spacers, so that, on each occasion when the buckle is used in heat pump mode air/air, the phenomenon may recur more frequently and more rapidly.

A spacer that is capable of being wider than the tubes and of which the upstream part, that is to say the part oriented towards the flow of air, lacks louvers, has been proposed according to a solution that is familiar from the prior art. Conversely, the downstream part of the spacer, that is to say the opposite part relative to the air inlet, has louvers. This makes it possible to limit the exchange with the air on the upstream part of the spacer due to the absence of a louver and, therefore, to control the icing.

The disadvantage of such a solution is to reduce the thermal exchange due to the absence of louvers over a large width of the spacer, resulting in a reduction in the efficiency.

According to another known solution, the spacer is likewise wider than the tube and has an assembly of small louvers, rather than a single full louver, over the entire height of the spacer on the upstream and downstream parts of the spacer.

A major disadvantage is that the water formed during the first deicing may stagnate between two folds in the upstream part of the spacer and increases the risk of accumulation of ice upstream of the exchanger.

The object of the invention is therefore to overcome at least partially these disadvantages of the prior art by proposing a spacer making it easier to control the formation of ice and to facilitate the flow of the condensate during deicing.

To this effect, the object of the invention is a spacer for an air heater, said spacer comprising a predefined number of planar walls that are substantially parallel and are connected two-by-two by folds, the planar walls including a plurality of louvers that are substantially inclined relative to the general plane defined by a planar wall, characterized in that a planar wall further includes at least one strap having longitudinal sides that extend parallel to the planar wall and lateral sides that are linked to the planar wall by means of at least one connecting rail.

With such a strap, the retention of water is reduced and the condensates flow more freely during deicing.

Said spacer may further include one or a plurality of the following characterizing features, either individually or in combination:

-   -   one planar wall has a substantially rectangular general form,         and the longitudinal sides of one strap extend in the direction         of the height of the planar wall,     -   one strap extends for a distance in the order of at least 75% of         the height of the planar wall,     -   one strap has a substantially strip-shaped general form defining         a plane substantially parallel to the plane defined by the         planar wall,     -   at least one strap is arranged at one extremity of the planar         wall intended to be oriented facing towards the inlet of a gas         stream in the air heater,     -   one planar wall includes at least two straps facing in two         opposite directions,     -   one planar wall includes at least two straps arranged in a         symmetrical manner on two opposite extremities of the planar         wall,     -   said louvers are arranged on a substantially central part of a         planar wall,     -   said spacer is formed from a metallic material and one strap is         produced by cutting and folding of the metallic material,     -   the planar walls respectively include at least two groups of         louvers having a respective orientation, the louvers of one         group being substantially identical,     -   said spacer has a substantially corrugated general form, the         planar walls being connected two-by-two by folds in such a way         as to form alternate corrugations.

The invention likewise relates to an air heater in which there circulates a fluid for a thermal exchange with a gas stream, said heater comprising a heat exchange bundle having a substantially parallelepipedic general form and comprising:

-   -   a stack of parallel tubes for the circulation of the fluid, the         tubes having the width of a tube, and     -   a plurality of spacers disposed respectively between two tubes         so as to be traversed by the gas stream, such that the spacers         have a width of a spacer greater than the width of a tube, in         such a way as to extend beyond the tubes, and respectively         comprise a predefined number of planar walls connected         two-by-two by folds, the planar walls including a plurality of         louvers that are substantially inclined relative to the plane         defined by the planar walls,         characterized in that a planar wall further includes at least         one strap having longitudinal sides that extend parallel to the         planar wall and lateral sides linked to the planar wall by means         of at least one connecting rail, and arranged on the upstream         extremity of the planar wall that is oriented facing towards the         inlet of the gas stream.

Other characterizing features and advantages of the invention will emerge more clearly from a perusal of the following description, which is provided by way of illustrative and non-restrictive example, and of the accompanying drawings, in which:

FIG. 1 is a frontal view of an air heater in particular for an automobile,

FIG. 2 a is a perspective view of a part of a spacer and of two adjacent tubes of the air heater in FIG. 1 according to a first variant,

FIG. 2 b is a partial side view of the spacer and of the two adjacent tubes in FIG. 2 a,

FIG. 2 c is a sectional view of the spacer in FIGS. 2 a and 2 b,

FIG. 3 depicts a graph illustrating the results of tests on a spacer with or without a strap, showing the retention of water over time during a first phase A of immersion of a sample of a spacer in water, and the evolution of the flow of the water during a second phase B of removal of the sample from the water,

FIG. 4 a is a partial side view of a spacer and of two adjacent tubes of the air heater according to a second variant,

FIG. 4 b is a sectional view of adjacent spacers in FIG. 4 a,

FIG. 5 a is a partial side view of a spacer and of two adjacent tubes of the air heater according to a third variant, and

FIG. 5 b is a sectional view of adjacent spacers in FIG. 5 a.

In these figures, the substantially identical elements bear the same references.

An air heater 1, in particular for an automobile, is depicted in a schematic manner in FIG. 1. In particular, such a heater may be intended for use in a hybrid and/or electric vehicle.

For example, this can be an external air heater of a conditioning system for heating or cooling the passenger compartment of the vehicle.

Such an external air heater is able to permit an exchange of calories between a fluid, in particular a heat transfer medium, and a gas stream as a flow of outside air.

The heat transfer medium is by way of example a refrigerant, such as tetrafluoroethane, known as R134a, carbon dioxide CO₂, or even tetrafluoropropene, known as HFO-1234yf.

Generally, an external air heater is installed on the front surface of the vehicle in such a way as to benefit from a dynamic air flow, in the form of a flow of outside air, when the vehicle is in motion.

The external air heater is capable of functioning as a condenser or as an evaporator, according to various modes of operation of the conditioning system.

In particular the external air heater may be used as a condenser in an air conditioning mode in order to cool the passenger compartment of the vehicle, and in evaporator in a heat pump mode in order to heat the passenger compartment. In evaporator mode, the external air heater makes it possible to extract calories in the form of heat from the flow of outside air. In condenser mode, the fluid releases heat to the flow of outside air passing through the external air heater.

Provision may also be made to operate the external air heater in condenser mode in an air conditioning mode in order to permit deicing of this external air heater.

In fact, when the external air heater has a temperature that is lower than that of the outdoor air, or even negative, the humidity of the outdoor air condenses and freezes on this external air heater. This is the case in particular when the external air heater is used as an evaporator when the conditioning system is being operated in heat pump mode.

The air heater 1 includes a heat exchange bundle 3.

The bundle 3 has a substantially parallelepipedic general form with a length L, a height h, and a width in the perpendicular direction in FIG. 1.

The bundle 3 comprises:

a stack of parallel tubes 5 and spacers 7 disposed between two tubes 5, and

two collector boxes 9, 11 for the fluid, namely one inlet box 9 and one outlet box 11.

The tubes 5 respectively have at least one channel for circulation of the fluid.

The tubes 5 are, for example, substantially longitudinal flat tubes, of which the length extends parallel to the length L of the bundle 3 (see FIG. 1).

Moreover, the tubes 5 discharge respectively via their opposite longitudinal extremities into the collector boxes 9 and 11. This permits the introduction of the fluid into the bundle 3 via the inlet box 9 and the removal of the fluid via the outlet box 11. These inlet collector boxes 9 and outlet collector boxes 11 are associated with a circuit for the fluid in which the heater 1 is installed.

The tubes 5 have a tube width or initial width l₁ (see FIGS. 2 a, 2 b) parallel to the direction of the width of the bundle 3.

The tubes 5 and the spacers 7 are metallic, for example. By way of example, provision may be made for tubes 5 and spacers 7 that are made from an aluminum alloy.

In particular, the spacers 7 may be formed from a metal strip, for example, from an aluminum alloy.

The tubes 5 and the spacers 7 may be brazed together.

The spacers 7 are interposed between the tubes 5 for circulation of the fluid in order to improve the thermal exchange between the gas stream F (see FIG. 2 b), such as the flow of outside air, and the fluid.

In fact, these spacers 7 disrupt the flow of the gas stream F and increase the thermal exchange surface between the fluid and the gas stream F.

The spacers 7 have a length extending parallel to the length L of the bundle 3.

The spacers 7 also have the width of a spacer or a second width l₂ parallel to the width l₂ of the tubes 5 and to the width of the bundle 3. This second width l₂ is greater than the first width l₂, so that the spacers 7 extend beyond the tubes 5.

In addition, the spacers 7 have a height h′ which defines the distance between two adjacent tubes 5.

The spacers 7 have, for example, a substantially corrugated general form. These are also referred to as spacers 7 folded in a concertina-like manner.

With reference to FIGS. 1 and 2 a, a spacer 7 comprises a predefined number of planar walls 13.

The planar walls 13 are substantially rectangular with a height h′ corresponding to the height h′ of the spacer 7.

These planar walls 13 are substantially parallel and are connected two-by-two by folds 15.

In the case of a corrugated spacer 7, as in the example illustrated here, the folds 15 are substantially rounded and the planar walls 13 are connected two-by-two by folds 15 in such a way as to form alternate corrugations.

The spacers 7 may be secured to the tubes 5 by their respective folds, for example by brazing.

In addition, the planar walls 13 include a plurality of louvers 17 ₁, 17 ₂ that are substantially inclined relative to the general plane P defined by the planar walls 13 (see FIGS. 2 a and 2 b).

These louvers 17 ₁, 17 ₂ respectively have a substantially blade-shaped general form.

The louvers 17 ₁, 17 ₂ may be produced by cutting and folding the metallic material of the spacer 7.

These louvers 17 ₁, 17 ₂ are, for example, arranged on a substantially central part of the planar wall 13. The louvers 17 ₁, 17 ₂ may also be disposed at right angles to the tube 5.

Provision may be made for two groups of louvers: a first group of louvers 17 ₁ and a second group of louvers 17 ₂. The louvers of the same group may be substantially identical.

Each group of louvers 17 ₁, 17 ₂ may have its own respective orientation. According to the example illustrated here, the louvers 17 ₁ of the first group are oriented, for example, towards the upstream part of the planar wall 13, whereas the louvers 17 ₂ of the second group are oriented towards the downstream part of the planar wall 13.

According to the embodiment described here, once the spacer 7 has been assembled in the air heater 1, the upstream part of the plane 13 is oriented facing towards the inlet for the gas stream F, and the downstream part of the planar wall 13 is thus opposite the inlet for the gas stream F.

Moreover, these louvers 17 ₁, 17 ₂ may extend for the entire height h′ of the planar wall 13.

The louvers 17 ₁, 17 ₂ therefore define openings according to a given angle of opening, through which the gas stream F passes, which increases the thermal exchange surface.

Furthermore, in addition to these louvers 17 ₁, 17 ₂, a planar wall 13 further includes at least one strap 19.

Such a strap 19 is produced, for example, by cutting and folding the metallic material of the spacer 7.

Once formed, for example, the strap 19 is offset relative to the plane P defined by the planar wall 13.

Such an offset d, or “offset” in English, is more clearly visible in FIG. 2 c. A sinking of material forming the strap 19 relative to the general plane P defined by the planar wall 13 can be noted, in fact. According to the example illustrated here, this sinking takes place in a manner perpendicular to the general plane P defined by the planar wall 13.

This offset d may be at least in the order of 0.1 mm. By way of example, provision may be made for an offset d in the order of 0.4 to 0.5 mm.

This strap 19 is arranged, for example, on at least one extremity of the planar wall 13. According to the example illustrated here, the planar wall 13 is substantially rectangular and the strap 19 is produced on one longitudinal extremity of the planar wall 13.

More precisely, the strap 19 is produced on one upstream extremity of the planar wall 13 intended to be oriented facing towards the inlet for the gas stream F during assembly of the air heater 1.

This arrangement of the strap 19 at the level of the inlet for the gas stream F into the air heater 1 is particularly advantageous since, in the case of icing, for example due to the use of the air heater 1 in evaporator mode, the accumulation of ice initially occurs upstream of the air heater 1. As will be described later, the strap 19 also makes it possible to reduce the formation of ice because the strap 19 is less prone to the retention of water, for example, relative to a louver 17 ₁, 17 ₂. The strap 19 thus helps to trap the moisture upstream.

As a variant or in addition, provision may be made for the spacer 7 to have at least one strap 19 on a downstream extremity, being intended specifically to be opposite the inlet for the gas stream in the air heater 1.

Furthermore, the strap 19 has, for example, a substantially strip-like general form. This strip defines a plane substantially parallel to the general plane P defined by the planar wall 13. For this reason, the planar wall 13 including such a strap 19 thus has a substantially rectangular hollow form.

By way of example, the width of this strap 19 may be in the order of at least 0.5 mm. Provision may be made, for example, for a width in the order of 2 mm.

The strap 19 has parallel and opposite longitudinal sides 21, and parallel and opposite lateral sides 23, so that the strap 19 is of substantially rectangular form.

The longitudinal sides 21 extend parallel to the planar wall 13 in the direction of the height h′ of the planar wall 13. This strap 19 may extend longitudinally for a distance of at least 75% of the height h′ of the planar wall 13, or for a distance corresponding to the full height h′ of the planar wall 13.

At least one of the longitudinal sides 21 of the strap 19 is intended to extend substantially at right angles to the gas stream F.

The lateral sides 23, for their part, are linked to the planar wall 13 by means of at least one connecting rail 24.

This strap 19 is therefore substantially parallel to the flow of the gas stream F, such as the flow of air; this makes it possible to reduce the loss of charge.

The presence of such a strap 19 makes it possible to control the formation of ice more effectively, especially in winter conditions when the air heater 1 is being operated as an evaporator in a heat pump mode. The reduction in the quantity of ice permits the exchange surface between the gas stream and the refrigerant to be increased, which makes it possible to improve the performance of the air heater 1. In addition, the strap 19 being planar, the condensates will flow more freely during deicing.

This is represented in a schematic manner in FIG. 3 illustrating the results of tests with the help of a sample of a spacer 7 equipped with straps 19 and a sample of a spacer without straps 19.

On the graph in FIG. 3, the first curve C1, identified with the help of diamonds, corresponds to a spacer 7 equipped with straps 19, and the second C2, identified with the help of triangles, corresponds to a spacer without straps 19; this latter spacer only has louvers 17 ₁, 17 ₂.

This graph illustrates:

-   -   a first phase A of immersion of a sample of a spacer 7 in the         water, so as to illustrate in a schematic manner the retention         of water in the spacer 7, and     -   a second phase B of removal of the sample of a spacer 7 from the         water, so as to illustrate schematically the flow of the water         that is retained over time.

By way of example, according to the test carried out, the first phase A of immersion is for a period in the order of 120 s. The second phase B commences at 120 s.

The graph 3 shows the time in seconds (s) on the horizontal axis and the weight of the water in the spacer in grams (g) on the vertical axis.

During the first phase A, it can be noted that the retention of water is greater in the spacer equipped with louvers 17 ₁, 17 ₂, but without straps 19. This is illustrated by the second curve C2, which increases more rapidly during this first phase A.

Conversely, the first curve C1 increases more slowly than the second curve C2. The retention of water is therefore less significant in the spacer 7 equipped with straps 19 than in the spacer without straps 19.

Therefore, the ice adheres less to a strap 19 than to a louver 17 ₁, 17 ₂.

Moreover, the Applicant has noted that the ice attaches less, the greater the offset d of the strap 19 relative to the general plane P defined by the planar wall 13.

Subsequently, when the sample is removed from the water, the flow is stronger in the spacer 7 equipped with straps 19 (see curve C1) due to the lower retention of water relative to the spacer without straps 19 (curve C2).

It will be appreciated, therefore, that the strap 19 makes it possible to reduce the formation of ice upstream of the spacer 7, and to improve the drainage of the condensates during the stage of deicing by operating the air heater 1 in condenser mode. In fact, the strap 19 is substantially parallel to the flow of the gas stream F passing through the air heater 1, which facilitates the flow of the condensates.

Spacers 7 having one strap 19 on the upstream extremities of the planar walls 13 have been described previously.

Provision may be made, as a variant, for more than one strap on an extremity of a planar wall 113, as illustrated in FIGS. 4 a and 4 b.

Provision may be made, for example, for two straps 119 ₁ and 119 ₂ on one upstream extremity of a planar wall 113.

The straps 119 ₁ and 119 ₂ are, for example, substantially identical in form to the strap 19 previously described with reference to FIGS. 2 a to 2 c, with longitudinal sides 21 and lateral sides 23 linked to the planar wall 113 by means of at least one connecting rail 24.

These two straps 119 ₁ and 119 ₂ may, for example, be produced in an opposing manner. This opposition of the two straps 119 ₁ and 119 ₂ is more clearly visible in FIG. 4 b. In order to do this, provision may be made for one of the straps 119 ₁ to be produced by sinking in a first direction indicated schematically by the arrow S₁ in FIG. 4 b, and the other strap 119 ₂ by sinking in a second direction S₂ opposite the first direction S₁. Thus, the sinking of the two straps 119 ₁ and 119 ₂ may take place in the direction perpendicular to the general plane P defined by the planar wall 13, but in two opposite directions S₁ and S₂. The two straps 119 ₁ and 119 ₂ thus formed are therefore oriented in two opposite directions S₁ and S₂.

The offset d or “offset” of the two straps 119 ₁ and 119 ₂ relative to the general plane P defined by the planar wall 113 may be substantially identical.

Finally, provision may likewise be made for one planar wall 113 to include at least one strap 119 ₁, 119 ₂, 119 ₃, 119 ₄ on the two opposite extremities of the planar wall (see FIGS. 5 a and 5 b). This design makes the production process for the spacer 7 easier.

In particular, provision may be made for at least two straps 119 ₁, 119 ₂, 119 ₃, 119 ₄ to be arranged in a symmetrical manner relative to the width l₂ of a spacer.

As previously stated, the planar wall 113 has a substantially rectangular general form, for example, and the two straps 119 ₁, 119 ₂, 119 ₃, 119 ₄ are supported, for example, by the two opposite longitudinal extremities of the planar wall 113.

In particular, a planar wall 113 may have at least two straps 119 ₁, 119 ₂, 119 ₃, 119 ₄ arranged respectively on the upstream extremity of the planar wall 113 that is intended to be oriented facing towards the inlet for the gas stream F in the assembled air heater 1, and on the downstream extremity of the planar wall 113 that is intended to be opposite this inlet for the gas stream F.

Provision may be made for the straps 119 ₁, 119 ₂, 119 ₃, 119 ₄ to be opposite two-by-two. More precisely, the two straps 119 ₁ and 119 ₂ on the upstream extremity of the planar wall 113 are oriented respectively in two opposite directions S₁ and S₂. Likewise, the two straps 119 ₄ and 119 ₃ on the downstream extremity are oriented respectively in the two opposite directions S₁ and S₂.

Thus, by way of example, when the straps 119 ₁, 119 ₂, 119 ₃, 119 ₄ are produced in a symmetrical manner, the two extreme straps 119 ₁ and 119 ₄ of the planar wall 113 are oriented respectively in the first direction S₁, whereas the two intermediate straps 119 ₂ and 119 ₃ are oriented respectively in the second direction S₂.

In addition, according to this variant embodiment, the louvers 17 ₁ and 17 ₂ are arranged, for example, on a substantially central part of the planar wall 113, and the straps 119 ₁, 119 ₂, 119 ₃, 119 ₄ are arranged to either side of these louvers 17 ₁ and 17 ₂.

It will be appreciated, therefore, that a spacer 7 for an air heater 1, in particular an external air heater, that is susceptible to becoming iced up, for example during the use of the air heater 1 in evaporator mode under winter conditions, and equipped with at least one strap 19, 119 ₁, 119 ₂, 119 ₃, 119 ₄, makes it possible to control the formation of the ice more effectively and to improve the flow of the condensates during switching of the function of the air heater 1 into condenser mode.

Such an air heater may comprise an upstream extremity of a planar wall 13 of a spacer provided with at least one strap 19, 119 ₁, 119 ₂ which projects beyond the tubes 5.

Such an air heater may also comprise a downstream extremity of a planar wall 13 of a spacer provided with at least one strap 119 ₃, 119 ₄ which is situated at right angles to at least one tube 5. 

1. A spacer for an air heater, the spacer comprising a predefined number of planar walls that are substantially parallel and are connected two-by-two by folds, the planar walls including a plurality of louvers that are substantially inclined relative to the general plane (P) defined by a planar wall, wherein at least one of the planar walls further includes at least one strap having longitudinal sides that extend parallel to the planar wall and lateral sides that are linked to the planar wall by means of at least one connecting rail.
 2. The spacer as claimed in claim 1, in which one planar wall has a substantially rectangular general form and the longitudinal sides of one strap extend in the direction of the height (h′) of the planar wall.
 3. The spacer as claimed in claim 2, in which one strap extends for a distance in the order of at least 75% of the height (h′) of the planar wall.
 4. The spacer as claimed in claim 1, in which one strap has a substantially strip-shaped general form defining a plane substantially parallel to the plane (P) defined by the planar wall.
 5. The spacer as claimed in claim 1, in which at least one strap is arranged at one extremity of the planar wall intended to be oriented facing towards the inlet of a gas stream (F) in the air heater.
 6. The spacer as claimed in claim 1, in which one planar wall includes at least two straps facing in two opposite directions.
 7. The spacer as claimed in claim 1, in which one planar wall includes at least two straps arranged in a symmetrical manner on two opposite extremities of the planar wall.
 8. The spacer as claimed in claim 1, in which the louvers are arranged on a substantially central part of a planar wall.
 9. The spacer as claimed in claim 1, formed from a metallic material and in which one strap is produced by cutting and folding of the metallic material.
 10. The spacer as claimed in claim 1, in which the planar walls respectively include at least two groups of louvers having a respective orientation, the louvers of one group being substantially identical.
 11. The spacer as claimed in claim 1, having a substantially corrugated general form, the planar walls being connected two-by-two by folds in such a way as to form alternate corrugations.
 12. An air heater in which there circulates a fluid for a thermal exchange with a gas stream (F), the heater comprising a heat exchange bundle having substantially parallelepipedic general form and comprising: a stack of parallel tubes for the circulation of the fluid, the tubes having the width (l₁) of a tube, and a plurality of spacers disposed respectively between two tubes so as to be traversed by the gas stream (F), such that the spacers have a width of a spacer (l₂) greater than the width of a tube (l₁) in such a way as to extend beyond the tubes, and respectively comprise a predefined number of planar walls connected two-by-two by folds, the planar walls including a plurality of louvers substantially inclined relative to the plane (P) defined by the planar walls, wherein at least one of the planar walls further includes at least one strap: having longitudinal sides that extend parallel to the planar wall and lateral sides linked to the planar wall by means of at least one connecting rail, and arranged on the upstream extremity of the planar wall that is oriented facing towards the inlet of the gas stream (F). 